>>What if 2 persons each preform [sic] a ritual to get the >>same thing?>>>>Witch [sic] one will get it than [sic]?

I assume you mean two people competing for the same thing. Obviously, two different people might have the same goal and both achieve it without any conflicts (e.g., both place a hex on the same third person, or may have desires of similar descriptions such as "a new job").

Even if we assume that the ritual work was the only means to a particular end, there are still so many factors to consider as to why a ritual may or may not work. These are outlined in the Book of Belial and essays such as The Combination Lock Principle. Most important in these cases I think is the "Balance Factor". If two people are competing for the same job position, and one person still does something very self-defeating (e.g., showing up for the interview dressed horribly or with a pretentious attitude) then that would obviously affect things greatly, no matter how many black candles you burn the night before.